The present invention relates to optical projection using diffraction for uses such as three dimensional (3D) surface measurements for facial recognition, motion detection, or other purposes.
Optical projection of a pattern is used in applications such as 3D surface measurements. The positions of a pattern of dots caused by beams projected onto a flat surface can be determined. When the same pattern of dots is projected on a 3D surface to be measured, the positions of the dots will deviate from their designed positions as a result of the different intersection height on the 3D surface. These deviations can be measured and correlated to the different distances, or depth, of the 3D surface, and a 3D image can be generated. Such a system can also be used for motion detection and other uses.
FIG. 1 shows an example application of a miniaturized optical projector for depth measurements. A smartphone 10 includes a display 12, a camera 14 and an internal processor and other electronics. Display 12 can be used for presenting information to a user, and also functions as a touch screen for inputting information. An optical projector/detector module 16 is provided. Projector/detector module 16 projects an IR image which diverges as shown by arrows 18. The IR image is projected onto a user's face 20 as a series of dots 22. A detector in optical projector/detector module 16 then detects the dots 22, and from their relative positions, can determine the depth of the various parts of the user's face 20. By combining this with traditional two dimensional facial recognition, a user's face can be detected with great accuracy.
One of the popular techniques for depth and/or motion sensing is to use an optical projector to cast an array of structured dots on an object. The detected image of the dots on the object allows the determination of the depth or the motion of the object.
One example of such an optical projector is described in Primesense U.S. Pat. No. 8,749,796. FIG. 2 is taken from FIG. 9A of such U.S. Pat. No. 8,749,796. A Vertical-Cavity Surface-Emitting Laser (VCSEL) array 100 is grown on a single wafer. The individual lasers are irregularly located on the wafer and grouped into one or more dot patterns. The lasers in each pattern are connected to a single electrode for excitation. The light beams from this VCSEL array 100 are then projected by a lens 120 (mounted on spacers 122) through a multiple beam grating (MBG) 124 onto a distant object. MBG 124, positioned by spacers 126, creates multiple replicas 128 of the pattern, VCSEL array 100 is in an integrated optical projection module 110. VCSEL die 100 is diced and mounted on a sub-mount 114 with electrical connections 116, 118. The electrical connections are coupled to die 100 by wire bonding conductors 122.
FIG. 3 is taken from FIG. 10A of U.S. Pat. No. 8,749,796 and shows the patterns of light dots cast on the object as an expanded pattern 160. Each of the distorted rectangular patterns (tiles) 162, centered on respective axes 164, is an image of the VCSEL array as illustrated by 166. Non-uniform patterns are used so that each projected dot can be correlated with a detected, reflected dot by the varying geometry.
A distinctly different optical projector was described in Hand Held Products US Pat. Appln. No. 2016/0377414, as shown in FIG. 4. A regular VCSEL array 1 was used as the light source. Each laser is collimated by a lens which is fabricated as a lenslet array 2 (an array of small lenses). These parallel collimated beams are focused by a lens 3 onto a Diffractive Optical Element (DOE) 4. The pattern 7 projected onto the object consisted of repeated images (sub-patterns 6) from the DOE. The separation of the repeated images is the result of each of the lasers in the array. In order to form the array of lights dots 5 on the object, all the lasers in the VCSEL array will be excited at the same time. The commonality of these two optical projectors is that they can cast mostly one structured dots patterns on the object.
In U.S. Pat. No. 8,749,796, the structured dots pattern is divided into two groups to reduce the heating effects on the VCSEL, allowing one group to be driven at higher power (See ¶0077). It would be desirable to have higher power lasers for longer distances, and to have a projector that is simpler to manufacture, without requiring a custom, irregular laser array.